Soot blower operation for vapor generator furnaces



June 28, 1966 E. 1.. KOCHEY, JR

SOOT BLOWER OPERATION FOR VAPOR GENERATOR FURNACES Filed Sept. 28, 196463 Id a .i||+mm.) w 46W wma m a n2 MW 5 N 6 M fm mwww s lHT 0M 55 4-iiiUii Z 5 wfwgfl lllfiii W 4 5 Z 5 497 i/ 1 ,1 J 31 2 5 s 3 r e 5 qmmw g 1 fl w /SIM J 0 B W o C fli l I I United States Patent 3,257,993580T BLOWER OPERATION FOR VAPOR GENERATOR FURNACES 1 Edward L. Kochey,.lr., Colehrook, Conn, assignor to Combustion Engineering, inc, Windsor,Corns, a corporation of Delaware Filed Sept. 28, 1964, Ser. No. 399,5589 Claims. (Cl. 122-392) This invention relates to soot blowers for aonce-through circuit vapor generator furnace and in particular to amethod and apparatus for selectively operating the soot blowers.

In a once-through circuit parallel tubes within the circuit must beconstrained in some manner to maintain the over-all structure. This maybe done by welding these tubes to bars which cross them transversely onthe casing side, or as is now often done by welding adjacent tubescontinuously throughout their length.

When an ash bearing fuel such as coal is burned within a steam cooledfurnace, ash and slag form on the walls of the furnace in an erraticpattern. This uneven slagging condition results in uneven heatabsorption which is refiected in an unbalance of the temperatures of thefluid passing through the furnace wall tubes. This temperature unbalancecreates a condition where the hotter tubes want to expand relative tothe cold tubes, setting up stresses in the over-all furnace wallstructure in various locations. Repeated slagging and cleaning of thefurnace walls will cause cycling of these stresses and may lead tofatique failures, even at relatively low stresses.

A circuit in such a situation may be controlled so that the outlettemperature is maintained constant regardless of the variations in heatabsorption. This may be accomplished by measuring the outlet temperatureand varying the relative flow through various groups of tubes inaccordance with the heat absorption of these parallel groups of tubes tomaintain the temperatures equal. In such a situation a group of tubesreceiving high heat absorption will contain the same temperature fluidas the other tubes but it will be operating at a higher heat absorptionrate. This higher heat absorption rate causes a higher metal temperaturein these circuits creating the same type expansion problem as previouslydiscussed although of lesser magnitude.

Normally in the operation of these units the over-all furnace dirtinessis sensed. This may be accomplished by measuring the gas temperatureleaving the furnace, measuring the steam temperature leaving aconvection heating surface of the unit, or measuring the position of asteam temperature controller. After this over-all dirtiness is sensed,the furnace wall soot blowers are operated in response to apredetermined amount of dirtiness. During this time the furnace may beoperating with a heavily slagged condition in one portion of the furnacewhile the remainder of the furnace is relatively clean. Such heavy localaccumulations of ash and slag lead to operating difliculties such asslagging of the burners, slagging up and plugging the superheaters, ordamage to the lower furnace when these slag masses become too heavy andfall from the walls.

It is an object of my invention to provide a method and apparatus forthe operation of furnace wall soot blowers in such a manner thatexcessive slag accumulations will not occur.

It is a further object to provide a method and apparatus for operatingsoot blowers in such a manner as to prevent excessive temperaturedifferentials throughout a furnace wall circuit.

It is a further object to provide a method and apparatus for operatingsoot blowers in a once-through circuit of a vapor generator furnace insuch a manner as to improve ice the distribution of temperatures in theelements of the circuit beyond that distribution which would exist in acompletely clean furnace by selectively des lagging areas of the furnacewall.

Other and further objects of the invention will become appirent to thoseskilled in the art as the description procee s.

With the aforementioned objects in view, the invention comprises anarrangement, construction and combination of the elements of theinventive organization in such a manner as to attain the resultsdesired, as hereinafter more particularly set forth in the followingdetailed p the stack (not shown).

description of an illustrative embodiment, said embodiment being shownby the accompanying drawing wherein the illustration depicts a sideelevation of a oncethrough vapor generator with soot blowers located inthe furnace walls and a schematic system illustrating the method andapparatus for operating the soot blowers.

In my invention a furnace wall circuit is divided into a plurality ofgroups of tubes, with particular soot blowers being associated with eachgroup. The heat absorbed in each group is determined in some manner suchas temperature or fluid flow measurements thereby indicating which ofthese groups have low heat absorption throughout their length. Theaverage heat absorption of all the groups of tubes within the section isalso obtained. The heat absorption of each particular group is thencompared to the average. When the heat absorption of a particular groupis a predetermined amount below the average, soot blowers associatedwith the particular group are activated cleaning the slag off the tubesof that particular group.

My invention therefore operates to maintain a uniform temperaturedistribution throughout a circuit. It may however actually improve thetemperature distribution through the furnace walls when amaldistribution exists for other reasons. Independent of ashaccumulation on the walls the distribution of combustion and gas flowpattern within the furnace may be such as to impose a particularly highheat absorption in certain sections of the furnace. According to myinvention these sections which tend to receive too much heat will bepermitted to slag up thereby decreasing the heat absorption in thosesections and increasing the uniformity of heat absorption throughout thefurnace. Maldistribution of temperatures within the section may alsooccur due to distribution of the fluid passing through the tubes. Thismay be caused by the characteristics of the supply piping which suppliesthe furnace wall tubes or by the particular configuration of theindividual tubes themselves. Again, my invention will permit those tubeswhich tend to have low flows, and are therefore operating hot, to slagup so that the temperature balance within the furnace is improved.

Fuel and air are delivered through the burners 2 into the furnace 3wherein the fuel is burned with the products of combustion passingthrough flue 4 discharging through Water is supplied at about 670 F. and4100 psi. to the side wall inlet header 5 as well as the front and rearinlet headers 7. The furnace 3 has its walls lined with a plurality ofvertical parallel tubes extending from the lower side wall header 5 tothe upper side wall header 8, and also from the lower front and rearwall headers 7 to the upper front and rear wall headers 9. Thewater inpassing through the furnace walls is heated to a temperature of about800 F. and leaves at a pressure of about 4000 psi.

This fluid, which may now be considered steam, is conveyed throughrelief lines 10 to crossover pipe 12 through which it is conveyed to thefinishing superheater section 13. This steam is then conveyed at atemperature of about 1000 F. through the steam pipe 14 to a steamturbine driving an electric generator (not shown).

Furnace wall soot blowers of the type illustrated in US.

Patent 2,662,241 are located in the furnace walls at three elevations,and are designated Row A, Row B and Row C. Each elevation contains sootblowers on all four walls of the furnace with the front and rear wallsbeing similar to the side walls, one of which is shown in theillustration. This wall has four blowers at each elevation. Theseblowers are operative to clean the furnace wall in the general area ofthe corresponding blower. Accordingly, the furnace wall circuit in theside wall is divided into four sections by means of division plates inthe upper header 8. Therefore one soot blower in each row corresponds toa particular group of tubes and when operated will claim a portion ofthese tubes.

Each group of tubes has a thermocouple and temperature transmitter 17associated with it. This is preferably located in the relief line sincethe steam from the various tubes within the group are mixed and thetemperature obtained is generally representative of each of the tubeswithin the group. Each of these temperature transmitters emits a controlsignal representative of the temperature measured through control line18 sending this signal to an auctioneering controller 19. Such acontroller is manufactured by and may be obtained from the Leeds &Northrup Company.

Steam temperature transmitter 20 by means of a thermocouple located inthe crossover pipe 12 determines the temperature of the fluid which isleaving the furnace wall circuit. Since this is a mixture of all thefluid leaving all the groups of tubes it represents the. averagetemperature for all groups of tubes. A control signal representative ofthis temperature passes through control line 22 to controller 23.

Flow meter 27 is located in the steam line 14 and senses the outputofthe steam generator. Controller 28 is associated with this flow meterand operates to emit a control signal to controller 23 through controlline 29 which is representative of an allowable temperature differencewhich may be varied as a function of load.

This control system operates so that the temperature leaving each of thegroups of tubes as sensed in accordance with temperature transmitters 17and compared with the average temperature as sensed by means oftemperature transmitter 20. When the temperature of any group of tubesis a predetermined amount below the average temperature, a soot blowerassociated with the particular group of tubes is to be operated. Thistemperature difference, which is desired, is not a fixed valuethroughout the load range but will vary depending on the output of theunit. This must be done in some designs since often it is found that thetemperature unbalance in furnace wall circuit is inherently higher atlower loads than at higher loads. Conversely on other units wherein thefurnace wall circuit operates as a portion of a recirculating system thetemperature unbalance may be inherently less at lower loads than athigher loads. In accordance with the particular design characteristicsof the units on which my invention is employed, controller 28 willoperate as a function generator emitting the desired temperaturedifference limitation in accordance with the steam fiow sensed by flowmeter 27.

This permissible temperature difference signal passing through controlline 29 is combined with the actual average temperature signal passingthrough control line 22 so that controller 23 emits a signal throughcontrol line 30 which is representative of a minimum acceptabletemperature. Each of the temperatures sensed by controller 17representing fluid temperature leaving each group of tubes is comparedin controller 19 to the minimum temperature signal passing throughcontrol line 30. When it is found that one of these temperaturesdecreases to the minimum acceptable value, a control signal is emittedthrough control line 32 to controller 33. This controller functions tooperate a soot blower corresponding to the particular group of tubeswhich have indicated a low temperature. It will alternately select asoot blower from Rows A, B

and C for the particular circuit; so that if the last blower blown inthat circuit were in Row A, Row B would now be selected with the nextselection being Row C.

The operating circuit for each of the soot blowers will include ablocking timer 35 which will operate to prevent the particular sootblower from operating within one hour of the time it was previouslyoperated. This will prevent continuous operation of a series of sootblowers when a low temperature is sensed leaving the particular circuitwhich is due to some cause other than heavy slagging in the area. Insuch a situation repeated operation of the soot blower on a wall that isalready clean would be useless and would consume expensive blowing mediaas well as creating possibilties of unnecessary tube erosion.

After the selected soot blower is operated in response to controller '33no further action will be taken directly in response to the initialdetermination of low temperature. However since controller 19 is stilloperating and comparing temperatures, it may sense that even after theoperation of this selected blower the temperature leaving the particulargroup of tubes is low. In this case the system will proceed aspreviously described with controller 33 selecting a soot blower in thenext row.

Thus the soot blowers will be operated in such a manner as to keep thewalls of the furnace generally clean 'by blowing those areas whichbecome excessively dirty as soon as they become dirty.

The described soot blower system operates to balance the heat absorptionwithin the furnace, but there is no provision to regulate the over-alldirtiness of the furnace. Therefore the gas temperature leaving thefurnace is sensed by gas temperature controller 37 which emits a controlsignal through control line 38 to controller 39. Flow meter 27 againsenses the steam flow of the unit with controller 40 emitting a controlsignal through control line 42 which is representative of the maximumdesired gas temperature for the particular load sensed. This controlsignal is compared to the actual gas temperature control signal incontroller 39. When the actual gas temperature exceeds the maximumallowable a controlling signal is emitted through control line 43 tocontroller 44 which in turn operates all the furnace wall blowers, thuseffecting a general cleaning of the furnace walls. This controller may,of course, respond to other means for sensing the over-all dirtiness ofthe furnace such as desuperheating spray quantity, amount of gasrecirculation or tilting burner position.

This controller 44 may function in several fashions. It may operate allthe soot blowers with no preferential selection being made. Alternately,as shown in the illustration, the control signal may be emitted fromcontroller 44 through control line 45 which passes to controller 28.Controller 28 is that controller which establishes the allowabletemperature difference as a function of the load of the steam generator.The control signal passing through control line 45 operates on thiscontroller to reduce the allowable temperature difference. In accordancewith the previously described scheme, the control signal emitted throughcontrol line 29 would function to operate soot blowers associated withgroups of tubes where the temperature difference between that group andthe average was more than the amount indicated as allowable by thecontrol signal passing through control line 29. Therefore by reducingthis allowable temperature difference, furnace wall soot blowers willoperate with a selection being made such that those soot blowersassociated with tubes having the lowest temperature will be operated.

When the gas temperature sensed by temperature transmitter 37 is reducedto an acceptable value for the particular load, there will be no needfor additional operation of soot blowers and the signal emitted bycontroller 44 through control line 45 reducing the allowable temperaturedifference will be stopped. Controller 28 will therefore function toperform its function of establishing the preprogrammed allowabletemperature difference.

While I have illustrated and described a preferred embodiment of myinvention it is to be understood that such is merely illustrative andnot restrictive and that variations and modifications may be madetherein without departing from the spirit and scope of the invention. Itherefore do not wish to be limited to the precise details set forth butdesire to avail myself of such changes as fall within the purview of myinvention.

What I claim is:

l. A vapor generator furnace; tubular surface lining the walls of saidfurnace; a plurality of groups of tubes connected in parallel comprisingat least a section of said furnace walls; means for passing fluid to beheated through said groups of tubes; at least one soot blower associatedwith each group of tubes; means for determining the average temperatureof the fluid leaving said furnace section; means for determining thetemperature of fluid leaving each group of tubes; means for comparingthe temperature of the fluid leaving each group of tubes with thetemperature of the fluid leaving said section; means for establishing apredetermined allowable temperature difference between the fluid leavingeach group of tubes and the fluid leaving the section; means responsiveto said comparing means for operating a soot blower associated with agroup of tubes when the difference between the temperature of the fluidleaving the corresponding group and the average temperature leaving saidsection exceeds said predetermined allowable temperature difference.

2. An apparatus as in claim 1 including: means for determining theoverall dirtiness of the furnace walls; means for operating the sootblowers in response to a first predetermined over-all dirtinesscomprising means for reducing the predetermined allowable temperaturedifference.

3. An apparatus as in claim 2 including: means for stopping operation ofthe soot blowers in response to a second over-all furnace dirtinesscomprising means for increasing the predetermined allowable temperaturedifference to its original value.

4. In a vapor generator furnace having a plurality of groups of tubeslining the walls of said furnace, the method of operation comprising:burning an ash bearing fuel within said furnace; passing fluid to beheated through said groups of tubes in heat exchange relationship withsaid burning fuel; sensing the temperature of the fluid leaving eachgroup of tubes; sensing the average temperature of the fluid leaving allgroups of tubes; comparing the temperature leaving each group of tubeswith that leaving all groups of tubes; and operating a soot blowercorresponding to a particular group of tubes when the temperatureleaving that group of tubes exceeds a predetermined amount below thetemperature leaving all groups of tubes.

5. A vapor generator furnace; tubular surface lining the walls of saidfurnace; a plurality of parallel groups of tubes comprising at least asection of said furnace walls; means for passing fluid to be heatedthrough said groups of tubes; at least one soot blower associated witheach group of tubes; means for determining the average heat absorptionof all the groups of tubes in said furnace section; means fordetermining the heat absorption of each group of tubes; means forcomparing the heat absorption of each group of tubes with the averageheat absorption of all the groups of tubes in said section;

means for establishing a predetermined allowable heat absorptiondifference between each group of tubes and average of all groups oftubes; means responsive to said comparing means for operating a sootblower associated with a group of tubes when the difference between theheat absorption of the corresponding group and the average heatabsorption of the groups within said section exceeds said predeterminedallowable heat absorption difference.

6. An apparatus as in claim 5 including: means for determining theover-all dirtiness of the furnace walls; means for operating the sootblowers in response to a first predetermined over-all dirtinesscomprising means for reducing the predetermined allowable heatabsorption difference.

7. An apparatus as in claim 6 including: means for stopping operation ofthe soot blowers in response to a second over-all furnace dirtinesscomprising means for increasing the predetermined allowable heatabsorption difference to its original value.

8. In a vapor generator furnace having a plurality of groups of tubeslining the walls of said furnace, the method of operation comprising:burning an ash bearing fuel within said furnace; passing fluid to beheated through said groups of tubes in heat exchange relationship withsaid burning fuel; sensing the heat absorbed by the fluid passingthrough each group of tubes; sensing the average heat absorbed by thefluid passing through all groups of tubes; comparing the heat absorbedby the fluid passing through each group of tubes with the average heatabsorbed by the fluid passing through all groups of tubes; and operatinga soot blower corresponding to a particular group of tubes when the heatabsorbed by the fluid passing through that group of tubes exceeds apredetermined amount below the aver-age heat absorbed by the fluidpassing through all groups of tubes.

9. A supercritical once-through vapor generator furnace comprising:vertical parallel tubes lining the walls of the furnace divided intoparallel groups of tubes; means for passing supercritical fluid throughsaid tubes; a soot blower associated with each group of tubes; means fordetermining the average temperature of the fluid lea'ving said tubes;means for determining the temperature of the fluid leaving each group oftubes; means for comparing the temperature of the fluid leaving eachgroup of tubes with the average temperature of the fluid leaving saidtubes; means for establishing a predetermined allowable differencebetween the temperature of the fluid leaving each group of tubes and theaverage temperature of the fluid leaving said tubes; means responsive tosaid comparing means for operating a soot blower associated with acorresponding group of tubes when the difference between the temperatureof the fluid leaving the corresponding group of tubes and the averagetemperature of the fluid leaving said tubes exceeds said predeterminedallowable difference.

References Cited by the Examiner UNITED STATES PATENTS 2,110,533 3/1938SHOW et al. l22392 2,811,954 11/1957 Hibner et al. 122---392 3,137,2786/1964 Cantieri et al. 122392 FREDERICK L. MATTESON, lR., PrimaryExaminer.

CHARLES J. MYHRE, Assistant Examiner.

1. A VAPOR GENERATOR FURNACE; TUBULAR SURFACE LINING THE WALLS OF SAIDFURNACE; A PLURALITY OF GROUPS OF TUBES CONNECTED IN PARALLEL COMPRISINGAT LEAST A SECTION OF SAID FURNACE WALLS; MEANS FOR PASSING FLUID TO BEHEATED THROUGH SAID GROUPS OF TUBES; AT LEAST ONE SOOT BLOWER ASSOCIATEDWITH GROUP OF TUBES; MEANS FOR DETERMINING THE AVERAGE TEMPERATURE OFTHE FLUID LEAVING SAID FURNACE SECTION; MEANS FOR DETERMINING THETEMPERATURE OF FLUID LEAVING EACH GROUP OF TUBES; MEANS FOR COMPARINGTHE THE TEMPERATURE OF THE FLUID LEAVING EACH GROUP OF TUBES WITH THETEMPERATURE OF THE FLUID LEAVING SAID SECTION; MEANS FOR ESTABLISHING APREDETERMINED ALLOWABLE TEMPERATURE DIFFERENCE BETWEEN THE FLUID LEAVINGEACH GROUP OF TUBES AND THE FLUID LEAVING THE SECTIONS; MEANS RESPONSIVETO SAID COMPARING MEANS FOR OPERATING A SOOT BLOWER ASSOCIATED WITH AGROUP OF TUBES WHEN THE DIFFERENCE BE-